The present invention relates to implantable medical devices which deliver energy to cardiac tissue for the purpose of maintaining a regular heart rate. Such devices are commonly referred to as cardiac pacing devices.
A remedy for people with slowed or disrupted natural heart beating is to implant a cardiac pacing device into the patient. A cardiac pacing device is a small electronic apparatus that stimulates the heart to beat at regular rates. It consists of a pulse generator, implanted in the patient""s chest, which produces electrical pulses to stimulate heart contractions. Electrical leads extend from the pulse generator to electrode placed adjacent to specific muscles of the heart, which when electrically stimulated produce contraction of the adjacent heart chambers.
Modern cardiac pacing devices adapt their pulse rate to adjust the heartbeat to the patient""s level of activity, thereby mimicking the heart""s natural beating. The pulse generator modifies that rate by tracking the activity at the sinus node of the heart or by responding to other sensors that monitor body motion and rate of breathing.
Different pacing needs are met by adjusting the programming of the pulse generator and by the location of the electrodes. It is quite common that the leads extend through veins which enter the heart so that the electrodes can be placed in the muscle of the heart chamber requiring stimulation. This requires that the leads extend for some distance through the veins and may also necessitate that the leads pass through one or two heart valves. In other patients, patch electrodes are placed on the exterior heart surface with wires extending through tissue to the pacing device. With either type of lead placement, it is important that the electrodes be attached to the proper positions on the heart to stimulate the muscles and produce contractions. Thus it is desirable to properly locate the electrodes for maximum heart stimulation with minimal adverse impact to other physiological functions, such as blood circulation.
An apparatus, for electrically stimulating tissue of an animal, comprises a generator which produces a stimulation signal having pulses occurring at a rate corresponding to a rate at which stimulation is desired. Where the stimulation controls the animal""s heart rate, the stimulation signal pulses occur at the heart rate that is desired for the animal. The stimulation signal is fed to a transmitter which emits a radio frequency signal.
An electrode-stent is implanted into a blood vessel of the animal at a location where the stimulation is desired, such as a blood vessel in a muscle of the heart. Upon receipt of the radio frequency signal the electrode-stent applies an electric current through tissue of the animal. In a preferred embodiment, the electrode-stent includes an antenna for receiving the radio frequency signal and a detector tuned to the frequency of the radio frequency signal. When the radio frequency signal is received, the detector produces an electric current that is applied to electrodes which in turn are in contact with the tissue to be stimulated.
The use of a radio frequency signal eliminates the need for hard wire connection between the source of the pacing signal and the stimulation electrodes. Therefore, a wire does not have to be permanently inserted through the vascular system of the animal.